1. Field of the Invention
This invention relates generally to centrifugal separators for separating mixed liquids of different densities, and more particularly to a self-cleaning rotor assembly for such separators.
2. Prior Art
Centrifugal devices are widely used for separating materials of different densities. Such devices have been found to provide a highly satisfactory method of separating liquids from one another based on different weight phases.
Separators, also referred to as extractors, can separate the individual components of a mixed component input stream, provided that the components remain in separate phases. In many instances, extraction may be facilitated with the use of a solvent that is injected into the device as a second input stream. In this case, the device is often referred to as a "contactor" since it brings the process stream and the solvent stream into intimate contact. The solvent phase, together with the soluble specie(s), is then separated from the carrier phase by differentiation of the phase densities. Typically, the process liquids comprise a lighter (less dense) solvent or organic phase and a heavier aqueous phase, which are introduced into the centrifugal contactor through separate inlets that communicate with a mixing zone. The resulting liquid mixture then enters the rotor of the contactor where centrifugal force separates the heavier phase from the lighter phase by forcing the heavier phase to flow outwardly away from the rotational axis of the rotor and thereby displace the lighter phase closer to the rotational axis of the rotor. The two phases are then individually collected at the upper end of the rotor with the heavier phase exiting at a location adjacent to the outer periphery and the lighter phase exiting at a location adjacent to the rotational axis. Typically, one or both of the exiting phases is subjected to one or more subsequent stages of extraction such as by circulation through another contactor.
A method of centrifugally separating the components of a water-petroleum mixture is described in U.S. Pat. No. 4,959,158 issued to the second-named inventor of this application. The method described therein utilized a centrifugal contactor developed by the U.S. Department of Energy for the extraction of transuranic elements from radioactive waste streams at nuclear processing plants. It was discovered that this device could be advantageously employed for the separation of a water-petroleum mixture. Improvements to the basic contactor design are disclosed in U.S. Pat. No. 5,591,340 and U.S. Pat. No. 5,571,070, both of which are commonly assigned with the present application.
The centrifugal separator disclosed in U.S. Pat. No. 5,591,340 employs a welded rotor assembly. During normal use, particularly when separating water/petroleum mixtures, solids suspended within the mixture tend to accumulate in the interior of the rotor assembly. Such solids are difficult to remove from a welded, enclosed rotor assembly. Backflushing of the rotor has not produced satisfactory results. Better results have been obtained by disassembling the separator and removing the rotor assembly. However, this is a time-consuming operation, thereby causing the separator to be removed from service for an extended period of time.